The present Core C (Cryopreservation and Stem Cell Biology Core), evolved from a predecessor devoted strictly to cryopreservation. Core C is far more sophisticated than its predecessor, and is already in full operation. The recent development of inducible pluripotent stem cell technology permits the regeneration of whole mice from individual cells with specific phenotypes, including cells identified through mutagenesis and phenotypic screening. The potential to screen the mammalian genome in depth for cell-autonomous phenotypes will be exploited in Project 1. Toward this end, the Core has already developed reprogrammable mice to facilitate the induction of iPS cells from a small population of MEFs selected for resistance to infection by Rift Valley Fever Virus (RVFV). Dedifferentiation is now routinely accomplished in our lab using doxycycline, once phenotypes of interest have been identified in mouse embryonic fibroblasts (MEFs). We will likely apply the same methodology to other cell types as well, including macrophages. Core C has already shown that mutagenized MEFs can be used to produce IPS cells, and in turn to produce viable mice that yield germline transmission of ENU-induced mutations. Other techniques have also been perfected to support the efforts of Project 1, and the exchange of mice between Osaka and Dallas. These include the use of intracytoplasmic sperm injection (ICSl) to force mapping crosses in low fertility strains, and the cryostorage of sperm, embryos, and IPS clones as needed for our collective work. A specialized facility for all of these techniques is essential for the success of Project 1, and the Program Project as a whole. This Core will facilitate the exchange of mice between Dallas and Osaka. RELEVANCE (See instructions): Core C has a dual function, permitting ultra-high efficiency mutagenesis of the mouse genome to find key proteins in the viral response and permitting rapid exchange of mice between Osaka and La Jolla. Both of these functions will contribute to public health by allowing the discovery of genes that impede viral proliferation and genes that are essential for it. This will allow deeper understanding of how viral infections progress and how they can be thwarted.